#container {
  text-align: center;
  margin: auto;
  width: 960px;
}

#container div {
  text-align: left;
}

#header, #main_content, #sidebar, #footer {
  margin: 10px;
}

#main_content {
  float: left;
  width: 700px;
}

#sidebar {
  float: left;
  width: 220px;  
}